Packing element for heat and mass transfer towers

ABSTRACT

A tower (A) for effecting heat transfer or chemical reactions contains a packing (B) formed from a multitude of packing elements ( 2, 28 ). Each element includes a peripheral wall ( 10, 30 ) and a convoluted interior wall ( 12, 32 ) that spirals inwardly from the peripheral wall toward the center of the element, thus forming a convoluted passage ( 14, 34 ) through the element. The convoluted passages in the elements capture the flow of fluid through the packing so that less fluid follows voids between the elements and more flows through the elements. Moreover, the convoluted interior wall of each element provides a large surface area for heat transfer or chemical reactions.

RELATED APPLICATION

This application derives priority from and otherwise claims the benefit of U.S. provisional application 61/080,050 filed 11 Jul. 2008, which application is incorporated herein by reference.

TECHNICAL FIELD

This invention relates in general to towers for effecting heat transfer or chemical reactions and, more particularly, to packing elements for such towers and to the towers containing such packing elements.

BACKGROUND ART

Many industrial processes utilize towers that contain random packings to effect the transfer of heat between the packing and gases that flow through such towers or to facilitate chemical reactions between different fluids that flow simultaneously through such towers. The traditional packing takes the form of saddle-shaped elements that are literally dumped into a tower where they assume random orientations. Where the tower is used for heat transfer, hot gases flow over and around the elements and elevate the temperature of the elements. They in effect become heat sinks. Afterwards, cooler gases flow through the tower and extract heat from the packing elements to elevate the temperature of those gases. The tower cycles back and forth between hot and cool gases. The large surface area on the elements enhances heat transfer. When a tower is used to promote chemical reactions between two fluids, which is referred to as mass transfer, the two fluids flow simultaneously through the tower. The large surface area created by the randomly arranged packing elements facilitates the chemical reaction. Generally speaking, the individual packing elements used for heat transfer are relatively small, while those used for mass transfer may be large or small.

Saddle-shaped packing elements impart a good measure of resistance to the flow of fluids in a tower and cause a corresponding pressure drop. To reduce the energy required to force fluids through such towers, the operators of some towers have turned to wafer-shaped elements, which reduce the pressure drop, yet maintain large surface areas for enhancing heat transfer or facilitating chemical reactions. The typical wafer-shaped element possesses a circular shape, but its diameter is considerably greater than its length. Internally, the element has septa that divide it into a multitude of small passages that extend through the element. The septa provide considerable surface area which is desirable. But the passages, being small, tend to restrict the flow of fluid and fail to capture the cross flow of fluid over the upstream faces of the elements.

That cross flow derives from the random orientation of the wafer-shaped elements. While the elements tend to orient themselves generally horizontally when dumped into a tower, many are inclined slightly. As a consequence, a void develops between any inclined element and a more horizontal element below or above it, so a packing comprised of numerous wafer-shaped elements will contain a multitude of voids between its elements. A fluid flowing through the tower tends to follow the voids as cross flow and not the small passages through the elements, inasmuch as the short margins that border the passages on the upstream faces fail to capture much of the cross flow. As a result, the large surface areas created by the septa are rendered less effective.

In towers containing monolith or structured media, the packing elements take the form of blocks stacked one upon the other. Typically, the blocks each contain a multitude of cells that are isolated from each other, so the air flow within any cell stays within that cell and cannot distribute across the block. The pressure drop and flow through the cells are not uniform, and this, in turn, results in poor utilization of the heat or mass transfer characteristics of the block-like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially broken away, of a tower containing packing elements constructed in accordance with and embodying the present invention;

FIG. 2 is a plan view of one of the packing elements;

FIG. 3 is a side elevational view of the packing element;

FIG. 4 is a sectional view of the packing element taken along line 4-4 of FIG. 2;

FIG. 5 is a plan view of a slightly modified packing element with webs;

FIG. 6 is a plan view of another slightly modified packing element with webs;

FIG. 7 is a sectional view taken along line 7-7 of FIG. 6;

FIG. 8 is a sectional view of another slightly modified packing element; and

FIG. 9 is a perspective view of packing elements in the form of a blocks constructed in accordance with the present invention.

BEST MODES FOR CARRYING THE INVENTION

Referring now to the drawings, a tower A (FIG. 1) contains a bed or packing B created by a multitude of packing elements 2 arranged randomly, but otherwise generally horizontally in the tower A. The packing B may serve to transfer heat between the packing B and gases that flow through the tower A or it may serve in a mass transfer capacity to enhance chemical reactions between the fluids that flow through the tower A simultaneously. To this end, the tower A has a shell 4 that confines the packing B and at least one port 6 at each end of the shell 4, and where the tower A is used for mass transfer, usually more than one port 6. so that different fluids may be introduced separately but simultaneously into the tower A.

Each packing element 2 possesses a unitary construction, that is to say it is formed as a single piece. It includes (FIGS. 2-4) a peripheral wall 10 that is circular or otherwise closes upon itself, thus establishing an axis X for the element 2. In addition, the element 2 has a convoluted interior wall 12 that creates and borders a convoluted passage 14 through the element 2. The interior wall 12 emerges from the peripheral wall 10 at a thickened region 16 of the peripheral wall 2 and spirals inwardly, terminating near the axis X of the element 2. The peripheral wall 10 and the convoluted interior wall 12 provide end surfaces 18 on the element 2, and those end surfaces 18 lie in planes that are parallel, the spacing between which represents the length of the element 2. The aspect ratio of element 2, that is the ratio of its diameter to its length (axial dimension), should range between about 2 and 6.

The element 2 may be provided in a variety of sizes from about 1.5 inches in diameter up to about 8.0 inches in diameter. The smaller sizes are preferred for heat transfer, whereas both small and large sizes are suitable for mass transfer. The material from which the element 2 is formed depends to a large measure on the fluids that pass through the packing B of which the element 2 is a part and the temperature of the fluids. The element 2 may be formed from a ceramic, from a metal, or from a polymer.

For most applications, the element 2 will be formed from a ceramic in an extrusion procedure. That procedure produces an extruded form from a suitable material. The form, upon emerging from the extrusion die, is cut with a blade or wire into individual green elements that are subsequently fired in a kiln or oven to produce the packing elements 2. Where a blade is used, it should enter the extruded form where the form is thickest, that is at the thickened region 16. The extrusion procedure is particularly suited for producing the elements 2 in smaller diameters, but it is also useful for larger diameters. However, in larger diameters, the green elements may be also produced by casting or molding, which from a technical perspective is preferred because it produces more accurate dimensions. However, it is more expensive than extruding.

To prevent a blade that cuts the extruded form into individual green elements from distorting those elements, each element 2 may be provided with webs 22 (FIG. 5) that span the convoluted passage 14 transversely from the thickened region 16 where the blade enters the extruded form. As such, the webs 22 connect the peripheral wall 10 with the largest convolution of the interior wall 12 as well as successive convolutions as of the interior wall 12. However, the webs 22, when so arranged, interrupt the convoluted passage 14 and divide it into foreshortened segments.

To minimize distortion during the cuts that sever the green elements from an extruded form, and yet leave the flow passage 16 without excessive interruptions, the webs 22 may be offset angularly in successive convolutions of the passage 16 so that they do not align across the element 2 (FIGS. 6 & 7). The webs 22 when so arranged strengthen the element 2. While the webs 22 still divide the passage 14 into segments, the segments are longer than when the webs 22 align across the element 2.

The elements 2 upon being dumped into the shell 4 of the tower A mostly assume horizontal or near horizontal orientations. Even so, many will be inclined slightly. Typically, an inclined element 2 will lie over a more horizontal element 2 or vice versa, creating a void between the end surfaces 18 on the two elements 2. Notwithstanding the void, fluids in that void upon encountering the convoluted wall 12 of the downstream element 2 will deflect at the edges along the upstream edges of the wall 12 and flow into the convoluted passage 14 bordered by the wall 12, inasmuch as the passage 14 extends for considerable length without interruption. It has its maximum length when it spirals all the way to the center of the element 2. Moreover, the fluid will tend to swirl through the passage 14, thereby enhancing contact between the fluid and the element 2, all with minimal pressure loss.

The peripheral wall 10 of the element 2 need not be cylindrical, although cylindrical is preferred. It may take an elliptical or other oblong configuration. Moreover, it may assume a polygonal configuration. In any one of those variations, the individual convolutions of the interior wall 4 and the passage 6 could assume the general shape of the peripheral wall 2.

Moreover, the element 2 may have two or more interior walls 12 and corresponding passages 14 that spiral inwardly from different locations along the peripheral wall 10—basically, one spiral within another.

When the element 2 is cast or molded, its interior wall 12 may have curved edges 24 (FIG. 8) at the end surfaces 18 and further may taper downwardly from the mid-region of the wall 4 to those edges 24, so that the wall 12 enlarges the ends of the convoluted passage 14, enabling the passage 14 to capture and direct more flow through the element 2.

In an alternative embodiment the peripheral wall 10 may be discontinuous, that is to say, it may have a short opening or slot in it. When so configured, the packing element 2 would more closely resemble a pure coil.

Polygonal configurations, preferably four-sided configurations, are suitable for monolith/structured packings C. Whereas the round packing elements are typically distributed randomly in a tower, monolith/structured packings typically include packing elements in the form of blocks 28 (FIG. 9) that are stacked one upon the other and side by side with little or no spacing between adjacent blocks 28, irrespective of whether they are over or under or to the side of another block 28. To this end, each block 28 has a peripheral wall 30 of polygonal shape and a convoluted interior wall 32 that establishes a convoluted passage 34 through the block 28. The convoluted passages 34 in the blocks 28 enable fluids to flow freely through the blocks 28 and further even out the pressure drop through different areas of the blocks 28, this in contrast to the typical monolith/structured blocks, which have separated passages or cells extending through them, with the cells being isolated from each other. A monolith/structured block 28 would typically measure 6×6×12 inches, with the longest dimension being in the axial direction and hence representing the length of the convoluted passage 34 through the block 28. 

1-19. (canceled)
 20. A packing element for effecting heat transfer or chemical reactions in a tower, said packing element comprising: a peripheral wall that establishes an axis; a convoluted interior wall that is connected to and spirals inwardly from the peripheral wall and terminates near the axis to provide a convoluted passage through the element; and webs attached to and connecting the peripheral wall and the largest convolution of the convoluted interior wall and also attached to and connecting convolutions of convoluted interior wall so as to interrupt the convoluted passage and divide it into segments; the packing element possessing a unitary construction and being formed from a ceramic material.
 21. A packing element according to claim 20 wherein the peripheral wall is uninterrupted and closes upon itself; and further comprising a thickened region where the interior wall merges with the peripheral wall.
 22. A packing element according to claim 20 wherein the webs are offset angularly so that they do not align across the element.
 23. A packing element according to claim 20 wherein the peripheral wall is circular.
 24. A packing element according to claim 23 having an aspect ratio of between about 2 and
 6. 25. A packing element according to claim 20 wherein the peripheral wall and interior wall have ends that lie in parallel planes.
 26. A packing element according to claim 20 wherein the interior wall has curved end edges.
 27. A packing element according to claim 26 wherein the interior wall is thickest between its curved end edges and tapers downwardly toward the curved end edges.
 28. A packing element according to claim 20 wherein the webs align transversely across the element.
 29. A packing element according to claim 20 that takes the form of a block in which the peripheral wall possesses a polygonal configuration; and wherein the convolutions of the interior wall also possess generally a polygonal configurations.
 30. A tower for effecting heat transfer or chemical reactions, said tower comprising: a shell having ports for introducing fluids into and delivering fluids from it; and a packing located in the shell and including a multitude packing elements in accordance with claim
 20. 31. A tower according to claim 30 wherein the packing elements are arranged randomly in the shell, with most being in a generally horizontal orientation. 